(1) Field of the Invention
This invention relates to lubricating apparatus, for example, to apparatus for lubricating fusing rolls used to fix toner-defined images in copying machines.
(2) Description of the Prior Art
Fusing systems in copying machines frequently use a heated fusing roll in conjunction with a backup roll. An advancing sheet of paper having toner applied to the surface in an electrophotographically-derived image pattern passes through the nip formed by the fusing roll and backup roll, where the image is fixed.
Offsetting of toner onto the fusing roll and concomitant sticking of the copy sheet to the fusing roll is a frequent problem in hot roll fusing processes. The result is degradation of the copy and decreased operating life for the fusing roll, as well as possible destruction of the copy and jamming of the machine. Offsetting and sticking can be alleviated by applying an elastomeric surface coating to the fusing roller to enhance toner release capability.
Release is also enhanced and the life of the roll extended by using a release lubricant such as silicone oil. Typically, the silicone oil release lubricant is applied to the fusing roll by a sponge-like and wick-like material which is immersed in a tank of silicone oil. Unfortunately, the use of such systems make it difficult to control the application of the silicone oil so that sufficient oil is applied to release the toner without staining the copy. Particularly after periods of inactivity, the silicone oil may build up excessively in the wick. Also, the wick tends to become clogged with toner and to lose effectiveness fairly quickly.
Various approaches have been used in attempting to improve the performance of wick-like applicators. For example, U.S. Pat. No. 3,718,116 to Raghulling A. R. Thettu; issued Feb. 27, 1973, uses an applicator roll to apply lubricant to a main wick contacting the fuser roll and uses an auxiliary wick to promote uniform application of the lubricant to the applicator. U.S. Pat. No. 3,831,553 to Raghulling A. R. Thettu; issued Aug. 27, 1974, utilizes a sponge inserted between the main wick, the auxiliary wick and the applicator roll of the aforementioned U.S. Pat. No. 3,718,116. A different approach is provided by U.S. Pat. No. 3,883,291, to Eugene F. Cloutier and Douglas P. Connolly; issued May 13, 1975, in that a wiper is applied directly to the fuser roll to remove excess release liquid applied by a sponge-like applicator. Also, the contact pressures of the wiper and the applicator against the fuser roll are varied to control the application of the liquid to the fuser roll and the effectiveness of the wiper.
U.S. Pat. No. 4,040,383 to Vandervort, assigned to Minnesota Mining and Manufacturing Company, teaches a non-wick-like, release lubricant applicator system which is durable and applies the release liquid uniformly, thus avoiding the problems associated with wick-like applicators and the necessity for resorting to complicating application systems for wick-like applicators.
The Vandervort apparatus comprises a lubricant-dispensing roll containing an internal supply of lubricant; an applicator roll for transferring lubricant from the dispenser roll to the fuser roll and for wiping the fuser roll; and a spreader roll for evenly distributing the lubricant on the applicator roll prior to the completion of transfer to the fuser roll. The dispenser roll has lubricant-dispensing apertures and a concentric inner cylinder which, during rotation of the roll, scoops lubricant contained therein into an annular reservoir formed between the roll and the inner cylinder. The reservoir provides a relatively constant head of lubricant so that the lubricant is dispensed uniformly over about 270.degree. of each revolution, regardless of the oil level in the dispenser roll. A fixed vent tube communicates with the interior of the dispenser roll to equalize pressure therein with the ambient and prevent heat-induced pumping of the lubricant.